refactor: remove shouldRun alias and add error isolation in ScheduleManager

[avoidwork]

Description

Remove redundant `shouldRun()` alias, clean up unused `_scheduler` parameter from `#clockTick`, and add try/catch error isolation around single-entry clockTick checks. Also updates docs/FLOWS.md to use `matchesCron` consistently.

Type of Change

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature which would cause existing functionality to not work as expected)
• Documentation update
• Refactor (no functional change)
• Performance improvement
• CI / build / tooling

Testing

All 961 tests pass. Four new test cases added:

• `#clockTick continues checking other entries if one throws` — verifies try/catch isolation keeps other entries running
• `#clockTick does not throw even with corrupted entries` — verifies no unhandled exceptions from bad data
• `#clockTick with 2 valid + 1 paused — all skip correctly` — verifies paused check still works alongside try/catch
• `#clockTick with 3 matching entries — only 1 deduped` — verifies try/catch does not break deduplication

Coverage

• 100% line coverage maintained

Checklist

• `npm run lint` passes
• Tests pass with 100% line coverage
• No forbidden patterns used
• Conventional Commit style applied